Mutations in the presenilin-1 (PS-1) gene are responsible for many cases of inherited early onset Alzheimer's disease (AD). Our preliminary data show that expression of mutant PS-1 in PC12 cells results in altered endoplasmic reticulum (ER) calcium regulation, which may be linked to increased of the cells to death induced by amyloid beta-peptide (Abeta) and trophic factor withdrawal (TFW). The proposed studies test the hypothesis that, by perturbing ER calcium homeostasis and stress responses, PS-1 mutations promote mitochondrial dysfunction, oxyradical production and neuronal degeneration. The first aim will test the hypothesis that the pro-apoptotic action of PS-1 mutations results from perturbed ER calcium homeostasis which promotes impaired mitochondrial function and increased oxyradical production. Mitochondrial functional parameters and oxyradical levels will be measured in PC12 cells and primary mouse hippocampal neurons expressing mutant or wild-type PS-1 following exposure of the cells to apoptotic insults. We will determine whether genetic and pharmacological manipulations block the pro- apoptotic actions of mutant PS-1. The second aim tests the hypothesis the IP/3 receptors play a key role in the pro-apoptotic action of mutant MS-1. We will examine the expression and subcellular localization of IP3R-3 in neurons (expressing wild-type or mutant PS-1) undergoing apoptosis; and determine whether IP3R-3 and PS-1 interact and whether PS-1 mutations affect the interaction. The third aim tests the hypothesis that the ER glucose-regulated proteins (grp78 and GRP94) play a role in protecting neurons against apoptosis. We will examine: the effects of apoptotic insults of grp78 and grp94) in protecting neurons against apoptosis. We will examine: the effects of apoptotic insults on grp78 and grp94 levels in neurons expressing wild-type or mutant PS-1; the consequence of grp78 and grp94 over-expression and "knock-out" on cellular vulnerability to apoptosis. The final aim tests the hypothesis that, by perturbing ER calcium homeostasis and inducing oxidative stress, PS mutations render neurons vulnerable to excitotoxicity in vivo. Injury to hippocampal neurons following administration of excitotoxins or 3NP to transgenic mice expressing wild-type or mutant PS-1 will be quantified. These studies will establish mechanisms responsible for adverse effects on PS-1 mutations on neuronal survival, and will identify targets for developing approaches to prevent neurodegeneration in AD.